Conventional belt retractors comprise a tensioning device having a cylinder and a piston slidably guided in the cylinder, the piston being provided with a tooth rack section into which a pinion can engage to drive the belt retractor.
Such a belt retractor is for example known from DE 44 15 103 A1. In case of this belt retractor, the tooth rack is integrated into the outer wall of the piston, so that the tensioning device can be constructed so as to have a very small size. The tooth rack is in engagement with the associated pinion already prior to the activation of the tensioning device and through the entire tensioning length. Therefore, a coupling is required, which connects the pinion to the retractor for the tensioning process and separates it afterwards so as to enable the belt webbing to be unwound from the belt reel. In DE 201 13 773 U1 the piston is provided with a vent valve in case of a belt retractor of the type concerned so as to enable the piston to be displaced again in the direction of its initial position after the tensioning process. This can be necessary, for example, for the function of a belt force limitation.
The invention provides a cost-effective and simple belt retractor comprising a tensioning device.